We propose to extend our recent preliminary observations in "new immigrant Yemenites" who had a low prevalence of diabetes (0.03%) in the years 1958-60 showing that in part of the families diabetes has become highly prevalent (9%) above the age of 30, while in other families no diabetes was detected. In families with diabetes, the diabetics consume significantly more mono and disaccharides than non-affected relatives of the same age and sex. Indicating the necessity for interaction between genetic and dietary factors for diabetes to be manifested, a result similar to our experimental observation where, by genetic selection, two strains of rats were inbred, one which after being fed a high fructose (1), glucose (2) or sucrose (3) diet develops diabetes, having common features with the human disease including vascular complications while the other strain fed the same diet remains normal. 700 more "new immigrant Yemenites" and 300 non-Yemenites as controls will be re-examined. Diabetes will be detected by an oral glucose tolerance (g.t.) the genetic familial tree and dietary intake - carbohydrate, mono and disaccharides, fat, protein and fiber - of each individual will be studied. We will also try to identify marker(s) of diabetes in the affected and non-affected families by the following tests: a) early phase of insulin release following i.v. g.t.; b) glucagon response; c) insulin receptors in blood granulocytes; d) blood lipids - beta lipoproteins, cholesterol, triglycerides and LDL; e) HLA antibodies and f) antipancreatic islet cells. The proposed study in a group with almost no diabetes 20 years ago that has changed to a Western environment and in which there are today families with a high prevalence of diabetes and families without diabetes is a unique group to study the interaction of the genetic factor(s) and the different factors related to the manifestation of diabetes such as sex, obesity, age, physical activity, dietary intake, and the different tests which may be used as indicators for the genetic susceptibility to diabetes.